The present invention generally relates to actuation mechanisms for use with deactivation and two-step roller finger followers (RFFs).
Deactivation RFFs typically include a body and a roller carried by a shaft. The roller is engaged by a cam of an engine camshaft that causes the RFF body to pivot, thereby actuating an associated engine valve. The deactivation RFF is selectively switched between a coupled and a decoupled mode of operation. In the coupled mode the shaft is coupled to the body, and rotation of the output cam is transferred from the roller through the shaft to pivotal movement of the RFF body, which, in turn, reciprocates the associated valve. In the decoupled mode, the shaft is decoupled from the body. Thus, the shaft does not transfer rotation of the output cam to pivotal movement of the RFF body and the associated valve is deactivated, i.e., not lifted or reciprocated, and therefore the term deactivation is used to describe this type of RFF. Zero-lift lobes on either side of the main cam engage and maintain the RFF body in a fixed position while in the decoupled mode of operation.
A two-step RFF operates in a manner similar to a deactivation RFF, as described above. However, rather than the body being engaged by zero-lift cam lobes as in the case of a deactivation RFF, the body of the two-step RFF is engaged by low-lift cam lobes. In the decoupled mode, the body of the two-step RFF is pivoted by the low-lift lobes thereby actuating the associated engine valve according to the lift profile of the low-lift cam lobes. In the coupled mode, the body of the two-step RFF is pivoted by the main cam thereby actuating the associated engine valve according to the lift profile of the main cam. Thus, the two-step RFF activates the associated valve according to a selected one of two different lift profiles, and therefore the term two step is used to describe this type of RFF.
The term RFF, as used hereinafter, encompasses both a deactivation RFF and a two-step RFF. Both types of RFFs are selectively switched between the coupled and decoupled modes of operation through the use of a locking pin assembly that couples and decouples the shaft to and from the RFF body. Typically, the locking pin assembly is a two-part pin that is biased by an associated spring into a default position, such as, for example, the decoupled position wherein the shaft is decoupled from the RFF body. In order to switch the locking pin assembly, and thus the RFF, between the coupled and decoupled modes, an actuating device is associated with the locking pin assembly. The actuating mechanism engages a trigger pin of the locking pin assembly to place and maintain the RFF in a first mode, such as, for example, the coupled mode. The actuating mechanism disengages from the trigger pin to thereby enable an internal spring of the locking pin assembly to bias the assembly into the second mode, such as, for example, the default/decoupled mode.
The actuating mechanism, such as, for example, a direct acting electro-mechanical solenoid or hydraulic actuator, engages the locking pin assembly to thereby place the locking pin assembly in one of the coupled and decoupled positions, such as, for example, the coupled position. In order to engage the locking pin assembly, an actuating mechanism must be disposed adjacent to the locking pin assembly of each RFF, and within the limited space available in the head of modern engines. Further, the actuating mechanism must provide sufficient force and stroke length in order to translate the locking pin mechanism, and thereby switch the mode of the RFF. Such direct acting mechanism require relatively large amounts of input power to initiate motion at relatively long distances. Moreover, the actuating mechanism must be precisely aligned with the locking pin assembly of the RFF in order to ensure smooth switching between modes.
Therefore, what is needed in the art is a device that enables the use of a smaller, less powerful actuating mechanism.
Furthermore, what is needed in the art is a device that reduces the distance over which the actuating mechanism must act, and thus reduces the amount of electrical current required to drive the actuating mechanism.
Moreover, what is needed in the art is a device that increases the alignment tolerance between the locking pin assembly of the RFF and the actuating mechanism.
The present invention provides a mechanical assist actuation bracket for use with a deactivation and/or two-step roller finger follower. The roller finger follower includes a locking pin assembly having a trigger pin.
The invention comprises, in one form thereof, a mechanical assist actuation bracket configured for being affixed to the roller finger follower. The bracket includes a face and an arm extending from the face. The arm is configured for translating an actuating arm of an actuating device associated with the roller finger follower in a direction toward and away from the trigger pin during pivotal movement of the roller finger follower.
An advantage of the present invention is that the bracket, by translating the actuating arm of the actuating device, reduces the power requirements of the actuating device thereby enabling the use of an actuating device having a reduced power rating and a smaller size. Another advantage of the present invention is that the bracket reduces the distances over which the actuating mechanism associated with the RFF must act, and thereby reduces the amount of electrical drive current required by the actuating mechanism.
Yet another advantage of the present invention is that the bracket increases the alignment tolerance between the actuating mechanism and the trigger pin of the locking pin assembly.
A still further advantage of the present invention is that mode switching of the roller finger follower occurs during the base circle phase of the cam event, and thus the switching event is self-timed.
An even further advantage of the present invention is that the mode switching event of the roller finger can utilize the entire base circle phase of the cam event, thus allowing substantial time for the switching event to occur.